Acids, particularly strong acids, have the ability to degrade a wide variety of substances normally found in drains. They hydrolyze proteins and celluloses and convert insoluble salts to soluble salts. They react with carbonates to liberate carbon dioxide, thereby producing turbulence, and they generate a fair amount of heat upon dilution with water. These are very desirable properties for drain cleaners. Similarly, acids are suitable for cleaning sulfide scales from metal surfaces, for example, from the interior of pipes in refinery installations. However, one of the major problems associated with the use of acid cleaner compositions, particularly as drain and pipe cleaners, is possible hydrogen sulfide liberation.
It has now been found that cations of the copper subgroup of the cation group 2 and some cations of the arsenic subgroup of the cation group 2 serve as scavengers for hydrogen sulfide (H.sub.2 S) when contained in acid cleaner compositions. When incorporated in acid cleaner compositions, the presence of these scavengers reduces the amount of hydrogen sulfide gas that is generated during the cleaning operation.
U.S. Pat. No. 4,220,550 to Frenier et al describes an aqueous acid composition for removing metal-sulfide scales from metal surfaces. The patentees also suggest the use of an aldehyde to prevent the evolution of H.sub.2 S. The use of the cations employed in this invention is not shown in Frenier et al. Moreover, the mechanism of H.sub.2 S scavenging that operates in the present invention obviously is far different from that in the case of Frenier et al as will be clear from the following disclosure.
U.S. Pat. No. 4,289,639 to Buske discloses an invention similar to that shown by Frenier et al. In Buske, glyoxylic acid is used to prevent the generation of hydrogen sulfide gas. In Martin, U.S. Pat. No. 4,276,185, chelating agents such as nitrilotriacetic acid, ethylenediaminetetraacetic acid and citric acid are used to protect against hydrogen sulfide evolution, the compositions in Martin having a pH between 8 to 10. The comments made above with regard to Frenier et al are also applicable to the Buske and Martin patents.